US20220126629A1 - Pneumatic radial tire - Google Patents

Pneumatic radial tire Download PDF

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Publication number
US20220126629A1
US20220126629A1 US17/310,440 US202017310440A US2022126629A1 US 20220126629 A1 US20220126629 A1 US 20220126629A1 US 202017310440 A US202017310440 A US 202017310440A US 2022126629 A1 US2022126629 A1 US 2022126629A1
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United States
Prior art keywords
cords
belt
pneumatic radial
steel
wire strands
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US17/310,440
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Inventor
Asuka Suzuki
Shinya Harikae
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Yokohama Rubber Co Ltd
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Yokohama Rubber Co Ltd
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Application filed by Yokohama Rubber Co Ltd filed Critical Yokohama Rubber Co Ltd
Assigned to THE YOKOHAMA RUBBER CO., LTD. reassignment THE YOKOHAMA RUBBER CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HARIKAE, SHINYA, SUZUKI, ASUKA
Publication of US20220126629A1 publication Critical patent/US20220126629A1/en
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Pending legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/18—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers
    • B60C9/20—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel
    • B60C9/2003—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel characterised by the materials of the belt cords
    • B60C9/2009—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel characterised by the materials of the belt cords comprising plies of different materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/0007—Reinforcements made of metallic elements, e.g. cords, yarns, filaments or fibres made from metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/0042—Reinforcements made of synthetic materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/02—Carcasses
    • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/18—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers
    • B60C9/20—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/18—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers
    • B60C9/20—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel
    • B60C9/22—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel the plies being arranged with all cords disposed along the circumference of the tyre
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/18—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers
    • B60C9/20—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel
    • B60C9/22—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel the plies being arranged with all cords disposed along the circumference of the tyre
    • B60C9/2204—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel the plies being arranged with all cords disposed along the circumference of the tyre obtained by circumferentially narrow strip winding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C2009/0071—Reinforcements or ply arrangement of pneumatic tyres characterised by special physical properties of the reinforcements
    • B60C2009/0078—Modulus
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C2009/0071—Reinforcements or ply arrangement of pneumatic tyres characterised by special physical properties of the reinforcements
    • B60C2009/0092—Twist structure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/02—Carcasses
    • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
    • B60C2009/0416—Physical properties or dimensions of the carcass cords
    • B60C2009/0433—Modulus
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/02—Carcasses
    • B60C9/04—Carcasses the reinforcing cords of each carcass ply arranged in a substantially parallel relationship
    • B60C2009/0416—Physical properties or dimensions of the carcass cords
    • B60C2009/0466—Twist structures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/18—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers
    • B60C9/20—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel
    • B60C2009/2074—Physical properties or dimension of the belt cord
    • B60C2009/2077—Diameters of the cords; Linear density thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/18—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers
    • B60C9/20—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel
    • B60C2009/2074—Physical properties or dimension of the belt cord
    • B60C2009/208—Modulus of the cords
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C9/00—Reinforcements or ply arrangement of pneumatic tyres
    • B60C9/18—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers
    • B60C9/20—Structure or arrangement of belts or breakers, crown-reinforcing or cushioning layers built-up from rubberised plies each having all cords arranged substantially parallel
    • B60C2009/2074—Physical properties or dimension of the belt cord
    • B60C2009/2083—Density in width direction

Definitions

  • the present technology relates to a pneumatic radial tire provided with a belt cover layer formed of organic fiber cords and particularly relates to a pneumatic radial tire that can improve durability while effectively reducing road noise.
  • a carcass layer is mounted between a pair of bead portions, a plurality of belt layers are disposed on an outer circumferential side of the carcass layer in a tread portion, and a belt cover layer including a plurality of organic fiber cords helically wound along a tire circumferential direction is disposed on an outer circumferential side of the belt layer.
  • Nylon fiber cords are mainly applied to the organic fiber cords used in the belt cover layer; however, in recent years, it has been proposed to use polyethylene terephthalate fiber cords (hereinafter referred to as PET fiber cords) that are highly elastic and inexpensive compared to nylon fiber cords (for example, see Japan Unexamined Patent Publication No.
  • the present technology relates to a pneumatic radial tire provided with a belt cover layer formed of organic fiber cords and particularly relates to a pneumatic radial tire that can improve durability while effectively reducing road noise.
  • a pneumatic radial tire includes: a tread portion extending in a tire circumferential direction and having an annular shape; a pair of sidewall portions respectively disposed on both sides of the tread portion; and a pair of bead portions each disposed on an inner side of the sidewall portions in a tire radial direction.
  • the pneumatic radial tire includes: a carcass layer mounted between the pair of bead portions; a plurality of belt layers disposed on an outer circumferential side of the carcass layer in the tread portion; and a belt cover layer disposed on an outer circumferential side of the belt layers.
  • the belt layers are formed of steel cords each having a 1 ⁇ M structure formed of M number of wire strands.
  • the M number of wire strands corresponds to one to six wire strands.
  • a tensile modulus of elasticity of the steel cords under 5 N to 50 N load is 130 GPa or more.
  • the steel cords are arranged inclined with respect to the tire circumferential direction to intersect each other in layers of the belt layers.
  • the belt cover layer is formed of organic fiber cords having elongation of 2.0% to 4.0% under 2.0 cN/dtex load. The organic fiber cords are wound helically along the tire circumferential direction.
  • the organic fiber cords having elongation of 2.0% to 4.0% under 2.0 cN/dtex load in the belt cover layer by using the organic fiber cords having elongation of 2.0% to 4.0% under 2.0 cN/dtex load in the belt cover layer, the frequency of vibration generated at the pneumatic tire when traveling can be shifted to a band that is less likely to resonate with a vehicle, the mid-range frequency road noise is reduced, and thus noise performance can be improved.
  • steel cords having the structure and physical properties described above and having a small initial elongation are used as the belt layer, separation in layers between the belt layer and the belt cover layer can be effectively prevented, and durability can be improved.
  • a steel cord amount A calculated as the product of a cross-sectional area S (mm 2 ) of the steel cord and a cord count E of the steel cords per 50 mm width orthogonal to a longitudinal direction of the steel cords (the number of cords per 50 mm) is preferably within a range of 5.0 to 8.0. Accordingly, the structure of the belt layer is appropriately set, and thus advantageously, separation in layers between the belt layers and the belt reinforcing layer is prevented and durability is improved.
  • the M number of wire strands preferably corresponds to two wire strands, and the steel cord is preferably set in a specification having a 1 ⁇ 2 structure.
  • the M number of wire strands preferably corresponds to one wire strand, and the steel cord is preferably set in a specification having a single-wire structure.
  • the organic fiber cords are preferably formed of polyester fibers.
  • road noise performance can be effectively increased by excellent physical properties (high elastic modulus) of the polyester fibers.
  • FIG. 1 is a meridian cross-sectional view illustrating a pneumatic radial tire according to an embodiment of the present technology.
  • FIG. 2 is an explanatory diagram schematically illustrating a structure of a belt cord.
  • a pneumatic tire of an embodiment of the present technology includes a tread portion 1 , a pair of sidewall portions 2 disposed on both sides of the tread portion 1 , and a pair of bead portions 3 disposed in the sidewall portions 2 at an inner side in a tire radial direction.
  • CL in FIG. 1 denotes a tire equator.
  • the tread portion 1 , the sidewall portions 2 , and the bead portions 3 each extend in a tire circumferential direction to form an annular shape.
  • a toroidal basic structure of the pneumatic tire is configured.
  • FIG. 1 is basically based on the illustrated meridian cross-sectional shape, all of the tire components each extend in the tire circumferential direction and form the annular shape.
  • a plurality of main grooves (four main grooves in the illustrated example) extending in the tire circumferential direction are formed in the outer surface of the tread portion 1 ; however, the number of main grooves is not particularly limited. Further, in addition to the main grooves, various grooves and sipes that include lug grooves extending in a tire width direction can be formed.
  • a carcass layer 4 including a plurality of reinforcing cords extending in the tire radial direction are mounted between the pair of left and right bead portions 3 .
  • a bead core 5 is embedded within each of the bead portions, and a bead filler 6 having a triangular cross-sectional shape is disposed on the outer periphery of the bead core 5 .
  • the carcass layer 4 is folded back around the bead core 5 from an inner side to an outer side in the tire width direction.
  • the bead core 5 and the bead filler 6 are wrapped by a body portion (a portion extending from the tread portion 1 through each of the sidewall portions 2 to each of the bead portions 3 ) and a folded back portion (a portion folded back around the bead core 5 of each bead portion 3 to extend toward each sidewall portion 2 ) of the carcass layer 4 .
  • a body portion a portion extending from the tread portion 1 through each of the sidewall portions 2 to each of the bead portions 3
  • a folded back portion a portion folded back around the bead core 5 of each bead portion 3 to extend toward each sidewall portion 2 ) of the carcass layer 4 .
  • polyester fiber cords are preferably used as the reinforcing cords of the carcass layer 4 .
  • a plurality (in the illustrated example, two layers) of belt layers 7 are embedded on an outer circumferential side of the carcass layer 4 in the tread portion 1 .
  • Each of the belt layers 7 includes a plurality of reinforcing cords 7 C that are inclined with respect to the tire circumferential direction, and the belt layers 7 are arranged such that the reinforcing cords 7 C intersect each other in the layers.
  • the inclination angle of the reinforcing cords 7 C with respect to the tire circumferential direction is set in the range of, for example, 10° to 40°.
  • Steel cords are used as the reinforcing cords 7 C of the belt layer 7 (in the following description, “reinforcing cords 7 C” may be referred to as “steel cords 7 C”).
  • each of the steel cords 7 C constituting the belt layer 7 includes a 1 ⁇ M structure (in the illustrated example, a 1 ⁇ 2 structure) that is formed of M number of wire strands 7 s.
  • the M number of wire strands 7 s corresponds to one to six wire strands.
  • the steel cord 7 C of an embodiment of the present technology has a 1 ⁇ 1 structure (that is, a single-wire structure) formed of the single wire strand 7 s or has a 1 ⁇ M structure formed by twisting the M number of wire strands 7 s (two to six wire strands) together.
  • the 1 ⁇ 1 structure (single-wire structure) and the illustrated 1 ⁇ 2 structure can be suitably employed.
  • the steel cord 7 C of an embodiment of the present technology has a tensile modulus of elasticity of 130 GPa or more under 5 N to 50 N load, and preferably has a tensile modulus of elasticity of 150 GPa to 200 GPa.
  • the tensile modulus of elasticity of the steel cords 7 C under 5 N to 50 N load is a numerical value obtained by dividing the inclination (load/strain) in the range of 5 N to 50 N load of the load-strain curve obtained when a tensile test is performed on the steel cords 7 C collected from the tire, by the sum of the cross-sectional areas of the wire strands 7 s constituting the cords.
  • a belt cover layer 8 is provided on an outer circumferential side of the belt layer 7 for the purpose of improving high-speed durability and reducing road noise.
  • the belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8 , the angle of the organic fiber cords with respect to the tire circumferential direction is set, for example, to from 0° to 5°.
  • the belt cover layer 8 necessarily includes a full cover layer 8 a that covers the entire region of the belt layers 7 , and can be configured to include a pair of edge cover layers 8 b that locally cover both end portions of the belt layers 7 as necessary (in the illustrated example, the belt cover layer includes both the full cover layer 8 a and the edge cover layers 8 b ).
  • the belt cover layer 8 is preferably configured such that a strip material made of at least a single organic fiber cord bunched and covered with coating rubber is wound helically in the tire circumferential direction, and desirably has, in particular, a jointless structure.
  • organic fiber cords constituting the belt cover layer 8 organic fiber cords having elongation of 2.0% to 4.0% under 2.0 cN/dtex load are used.
  • the type of organic fibers constituting the organic fiber cords is not particularly limited, and for example, polyester fibers, nylon fibers, aramid fibers, or the like can be used. Out of the fibers, polyester fibers can be suitably used. Additionally, examples of the polyester fibers include polyethylene terephthalate fibers (PET fibers), polyethylene naphthalate fibers (PEN fibers), polybutylene terephthalate fibers (PBT), and polybutylene naphthalate fibers (PBN), and PET fibers can be suitably used.
  • PET fibers polyethylene terephthalate fibers
  • PEN fibers polyethylene naphthalate fibers
  • PBT polybutylene terephthalate fibers
  • PBN polybutylene naphthalate fibers
  • the elongation under 2.0 cN/dtex load is an elongation ratio (%) of sample cords, which is measured under 2.0 cN/dtex load by conducting a tensile test in accordance with JIS (Japanese Industrial Standard)-L1017 “Test Methods for chemical fiber tire cords” and under the conditions that a length of specimen between grips is 250 mm and a tensile speed is 300 ⁇ 20 mm/minute.
  • JIS Japanese Industrial Standard
  • the belt layers 7 formed of the steel cords 7 C having a specific structure and specific physical properties and the belt cover layer 8 formed of organic fiber cords having specific physical properties are used in combination, and thus durability can be improved while road noise performance is improved.
  • the belt cover layer 8 due to the physical properties of the organic fiber cords, the frequency of vibration generated at the pneumatic tire when traveling can be shifted to a band that is less likely to resonate with a vehicle, and road noise performance can be improved.
  • the steel cords 7 C having the structure and physical properties described above and having a small initial elongation are used, and thus separation in layers between the belt layers 7 and the belt cover layer 8 can be effectively prevented, and durability can be improved.
  • the steel cord amount A is preferably within the range of 5.0 to 8.0. Accordingly, the structure of the belt layer is appropriately set, and thus advantageously, separation in layers between the belt layers and the belt reinforcing layer is prevented and durability is improved.
  • the steel cord amount A is less than 5.0, the proportion of the steel cords 7 C occupied in the belt layers 7 decreases, and thus steering stability may decline.
  • the numerical range of the cross-sectional area S of the steel cord 7 C or the cord count E of the steel cords 7 C is not particularly limited, but the cross-sectional area S of the steel cord 7 C can be set at, for example, 0.08 mm 2 to 0.30 mm 2 and the cord count E can be set at, for example, 20 cords/50 mm to 60 cords/50 mm.
  • PET fiber cords polyethylene terephthalate fiber cords
  • PET fiber cords having an elastic modulus in a range of 3.5 cN/(tex ⁇ %) to 5.5 cN/(tex ⁇ %) under 44 N load at 100° C. is preferably used.
  • the PET fiber cords having specific physical properties are used, and thus road noise can be effectively reduced while durability of the pneumatic radial tire is maintained successfully.
  • the elastic modulus of the PET fiber cords under 44 N load at 100° C. is less than 3.5 cN/(tex ⁇ %), the mid-range frequency road noise cannot be sufficiently reduced.
  • the elastic modulus under 44 N load at 100° C. [N/(tex %)] is calculated by: conducting a tensile test with reference to “Test Methods for chemical fiber tire cords” of JIS-L1017 and under the conditions that a length of specimen between grips is 250 mm and a tensile speed is 300 ⁇ 20 mm/minute; and converting the inclination of the tangent, at a point corresponding to load 44 N of the load-elongation curve, to a value per 1 tex.
  • heat shrinkage stress of the PET fiber cords at 100° C. is preferably 0.6 cN/tex or more.
  • the heat shrinkage stress at 100° C. is set as just described, and thus road noise can be effectively reduced while durability of the pneumatic radial tire is maintained successfully.
  • the heat shrinkage stress of the PET fiber cords at 100° C. is less than 0.6 cN/tex, the hoop effect when traveling cannot be sufficiently improved, and it is difficult to sufficiently maintain high-speed durability.
  • the heat shrinkage stress (cN/tex) at 100° C. is heat shrinkage stress of a sample cord, which is measured with reference to “Test Methods for chemical fiber tire cords” of JIS-L1017 and when heated under the conditions of the sample length of 500 mm and the heating condition at 100° C. for 5 minutes.
  • the PET fiber cords having the aforementioned physical properties for example, it is preferable to optimize dip processing.
  • dip processing with adhesive is performed on the PET fiber cords; however, in a normalizing process after a two-bath treatment, it is preferable that an ambient temperature is set within the range of 210° C. to 250° C. and cord tension is set in the range of 2.2 ⁇ 10 ⁇ 2 N/tex to 6.7 ⁇ 10 ⁇ 2 N/tex. Accordingly, desired physical properties as described above can be imparted to the PET fiber cords.
  • the cord tension in the normalizing process is smaller than 2.2 ⁇ 10 ⁇ 2 N/tex, cord elastic modulus is low, and thus the mid-range frequency road noise cannot be sufficiently reduced.
  • cord tension is greater than 6.7 ⁇ 10 ⁇ 2 N/tex, cord elastic modulus is high, and thus fatigue resistance of the cords is low.
  • Tires according to Conventional Example 1, Comparative Examples 1 to 4, and Examples 1 to 10 were manufactured.
  • the structure of each of the steel cords constituting the belt layers; the tensile modulus of elasticity of the steel cords under 5 N to 50 N; the steel cord amount A calculated as the product of the cross-sectional area S of the steel cord and the cord count E of the steel cords per 50 mm width orthogonal to the longitudinal direction of the steel cords; the type of organic fibers used in the organic fiber cords that constitute the belt cover layer; and the elongation of the organic fiber cords under 2.0 cN/dtex load are differentiated as in Tables 1 and 2.
  • the belt cover layer includes a jointless structure in which a strip material made of at least a single organic fiber cord (nylon 66 fiber cord or PET fiber cord) bunched and covered with coating rubber is wound helically in the tire circumferential direction.
  • the cord count density in the strip material is 50 cords/50 mm.
  • each organic fiber cord (nylon 66 fiber cord or PET fiber cord) has a structure of 1100 dtex/2.
  • N66 nylon 66 fiber cords
  • PET fiber cords PET fiber cords
  • Each of the test tires was assembled on a wheel having a rim size of 18 ⁇ 7 J, mounted as front and rear wheels of a passenger vehicle (front wheel drive vehicle) having an engine displacement of 2500 cc, and inflated to an air pressure of 230 kPa, and a sound collecting microphone was placed on an inner side of the window of a driver's seat.
  • a sound pressure level near the frequency 315 Hz was measured when the vehicle was driven at an average speed of 50 km/h on a test course of an asphalt road surface.
  • the evaluation results were based on Conventional Example as a reference and indicated the amount of change (dB) to the reference. Note that when the amount of change is 0 dB to ⁇ 1 dB, that means the effect of reducing road noise is substantially not obtained.
  • Each of the test tires is mounted on a rim having a rim size of 18 ⁇ 7 J and held in a chamber held at room temperature 70° C. for two weeks with oxygen filled at an internal pressure of 280 kPa, and then the inside oxygen is released and air is filled at 170 kPa.
  • test tires previously treated as just described were driven 5000 km for 100 hours by varying the load and slip angle with a rectangular wave of 0.083 Hz, under the conditions of an ambient temperature controlled to 38 ⁇ 3° C., a travel speed of 50 km/h, a slip angle within 0 ⁇ 3°, and a variation within 70% ⁇ 40% of the JATMA (The Japan Automobile Tyre Manufacturers Association, Inc.) maximum load.
  • JATMA The Japan Automobile Tyre Manufacturers Association, Inc.
  • a case where the amount of separation is 3 mm or less is “good”, a case where the amount of separation is greater than 3 mm and 5 mm or less is “pass”, and a case where the amount of separation is greater than 5 mm is “fail”.
  • the evaluation results are “good” or “pass”, that means sufficient durability is obtained, and “good” indicates particularly excellent durability.
  • test tires were assembled on wheels having a rim size of 18 ⁇ 7 J, mounted as front and rear wheels of a passenger vehicle (front wheel drive vehicle) having an engine displacement of 2500 cc, and inflated to an air pressure of 230 kPa.
  • Sensory evaluations for steering stability were made by five test drivers on a test course of a dry road surface. The evaluation results were scored by a 5-point method with the results of Conventional Example 1 being assigned 3-point (reference), and an average value of the scores of the three test drivers, with the exception of the highest point and the lowest point, was indicated. Larger points indicate superior road noise performance (sensory measurements).
  • Example 1 Belt Structure of steel 1 ⁇ 3 ⁇ 0.28 1 ⁇ 3 ⁇ 0.28 1 ⁇ 2 ⁇ 0.30 layers cords Tensile modulus GPa 90 90 150 of elasticity Steel cord 6.3 6.3 6.0 amount A Belt Type of organic N66 PET N66 cover fibers layer Elongation under % 7.5 2.8 7.5 2.0 cN/dtex load Road noise performance dB 0.0 ⁇ 2.0 0.0 Durability Good Fail Good Steering stability 3.0 3.2 3.0 Example Example 1 2 Example 3 Belt layers Structure of steel cords 1 ⁇ 2 ⁇ 0.30 1 ⁇ 3 ⁇ 0.28 1 ⁇ 1 ⁇ 0.345 Tensile modulus of elasticity GPa 150 130 200 Steel cord amount A 6.0 6.3 6.0 Belt cover Type of organic fibers PET PET PET layer Elongation under 2.0 % 3.0 3.0 3.0 cN/dtex load Road noise performance dB ⁇ 2.0 ⁇ 2.1 ⁇ 2.1 Durability Good Good Good Good Steering stability 3.2 3.0 3.0
  • Comparative Example 3 since the elongation of the belt cover layer under 2.0 cN/dtex is too small, separation between the belt layers and the belt cover layer cannot be prevented, and thus sufficient durability is not attained. In Comparative Example 4, since the elongation of the belt cover layer under 2.0 cN/dtex load is too large, the effect of improving road noise performance is not sufficiently attained, and in addition, steering stability is declined.

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